Port conceded a last-gasp goal to let former champions Chiang Rai United off the hook in a 1-1 home draw in Thai League 1 on Sunday night.
Port's goal came early in the first half in a dramatic fashion.
The Beetles goalkeeper Saranon Anuin cleared a shot back to Hamilton Soares after Kewin Deeromram set up the Brazilian in the 20th minute. Hamilton pounced on the second chance to chip the ball over Saranon.
Felipe Amorin grabbed the equaliser for Chiang Rai in the sixth minute of injury time.
Muang Thong United relieved their coach Mario Gjurovski of further pressure with a second straight 5-0 triumph.
The Kirins showed struggling Lamphun Warriors no mercy as they raced to a 2-0 advantage through two first-half goals from Henri Anier.
Muang Thong started the second half in a confident mood and got their third goal of the match through Porramet Arj-vilai three minutes after the break.
An Ekanit Panya cross in the 65th minute found Sardor Mirzaev who headed home with ease and Eric Johana beat an off-side trap to complete the rout eight minutes from time.
On Saturday night, former champions BG Pathum United dropped points again following a 2-2 home draw with Lampang while hosts Chonburi also settled for one point after being held 1-1 by Sukhothai.